1. Field of the Invention
The present invention relates to an image reading apparatus and an image forming apparatus including a hinge device that supports an opening/closing member such as an automatic document feeding device, which automatically sends an original to an image reading portion, to be opened or closed with respect to the apparatus main body of the image reading apparatus or the image forming apparatus.
2. Description of the Related Art
Conventionally, in a copying machine in which an automatic document feeding device is mounted, in a case where an original is copied, the automatic document feeding device disposed to be freely opened or closed with respect to transparent glass (hereinafter, referred to as an original base plate glass) disposed on the upper face of the apparatus main body is used in a closed state. Accordingly, the automatic document feeding device sequentially conveys originals to the original base plate glass in which an image reading portion is placed one at a time, and the originals can be automatically read one by one. In addition, instead of using the automatic document feeding device, by opening the automatic document feeding device to the apparatus main body, an original may be directly placed on the original base plate glass so as to be read.
In the automatic document feeding device, in order to automatically convey an original, many components such as various rollers and motors are built. Accordingly, the weight of the automatic document feeding device is several kilograms to several tens of kilograms, and an opening or closing operation cannot be easily performed as it is. Thus, generally, an opening/closing mechanism called a hinge device used for decreasing an operation force is included.
The hinge device has a spring built therein and applies a force in a direction opening the automatic document feeding device, in other words, a direction cancelling the weight (hereinafter, referred to as a “self-weight”) of the automatic document feeding device. Accordingly, the balance between the spring and the self-weight is set such that the automatic document feeding device can be lifted with a weak force at the time of opening and can be quietly closed at the time of closing.
In addition, there is an automatic document feeding device that includes a shock absorber that is an impact mitigating portion such as an oil damper in the hinge device. Since the oil damper generates a resistance force against the direction in which the automatic document feeding device is closed, there is an advantage of decreasing the closing speed of the automatic document feeding device so as to reduce a shock or a sound generated in accordance with the collision thereof with the apparatus main body. Accordingly, not only the original base plate glass, a driving portion of the automatic document feeding device, and the like are protected, but also oscillation delivered to the image forming apparatus is reduced, whereby disturbances in an image at the time of forming the image can be prevented.
In addition, as disclosed in Japanese Patent Laid-Open No. 3-184059, in order to easily replace an original on the original base plate glass, even when the hand is separated from the open automatic document feeding device, the automatic document feeding device is set to stay at the position (hereinafter, this state will be referred to as free stop). Furthermore, in order to maintain a state in which the automatic document feeding device securely lands on the original base plate glass, balance between the spring and the self-weight is set. FIGS. 17A and 17B illustrate a conventional example. FIG. 17A is a simplified view that illustrates each opening/closing angle state, and FIG. 17B is a diagram that represents the “magnitude relation between the spring and the self-weight” at each opening/closing angle converted into moment.
For example, a state in which the ADF (automatic document feeding device) is closed with respect to the original base plate glass disposed on the reader (image reading apparatus) side is represented as 0 degrees, and a vertical state is represented as 90 degrees. At this time, in a case where the opening/closing angle is in the range of 15 degrees to 70 degrees, a state is formed in which the spring and the self-weight are balanced, and thus, when the automatic document feeding device is in the free stop state, and the hand is separated therefrom, the automatic document feeding device does not fall in accordance with the self-weight. In addition, when the automatic document feeding device is opened up to 90 degrees, a case where a handle (a knob at the time of opening or closing) is not reached by the hand at the time of closing, a case where an impact is applied to the hinge device, or the like may be caused. Thus, actually, the opening angle of the automatic document feeding device is configured to be limited up to 70 degrees.
Furthermore, in a case where the opening/closing angle is in the range of 0 degrees to 15 degrees, a state is configured to be formed in which the spring<the self-weight, so that the automatic document feeding device falls in accordance with the self-weight. Accordingly, the automatic document feeding device is configured not to be stopped in the state in which the automatic document feeding device is about half open with respect to the original base plate glass. By configuring the spring force of the hinge device to be sufficiently weaker than the self-weight of the automatic document feeding device, the automatic document feeding device securely lands on the original base plate glass.
When the automatic document feeding device does not securely land on the original base plate glass but is in a half-open state, the pressing force for the original placed on the original base plate glass is lowered, and accordingly, a defective image is generated, or a paper jam occurs when the automatic document feeding device is used. Accordingly, generally, the self-weight is set to be stronger than the spring force by about 2 to 3 Kgf as a whole at the position of the handle of the automatic document feeding device, and the state in which the automatic document feeding device is approximately half-open is avoided.
However, in the configuration disclosed in Japanese Patent Laid-Open No. 3-184059 or illustrated in FIGS. 17A and 17B, the state of closing the original base plate glass is assured by setting the self-weight of the automatic document feeding device to be larger than the spring force, and accordingly, a force of about 2 to 3 Kgf is necessary for opening the automatic document feeding device. Thus, there is a limit on the decrease in the opening/closing force.